Conventionally, as a conductor of an electrical wire for wiring in automobiles, robots, electrical/electronic equipments, and the like, the followings have been mainly used: an electrical annealed copper wire, as stipulated under JIS C 3102; or an electrical wire (coated electrical wire) obtained by stranding plated wires, which are each obtained by plating that annealed copper wire with tin, or the like, to give a stranded wire, and covering the resultant stranded wire with an insulating substance, such as vinyl chloride or crosslinked polyethylene.
When those electrical wires are connected to an equipment, a terminal called a crimping terminal (or solderless terminal) is generally connected to the electrical wires by crimping, and then the thus-crimped terminal connected to the electrical wires is connected to the equipment. The crimping connection is a method of wrapping electrical wires in (or sandwiching those with) a terminal material, and then caulking (or fastening) the material, to ensure electrical connection.
As a method of evaluating the state of connection by crimping, there is a method of testing on the basis of “Tensile Strength of Crimp Contact” in JIS C 5402 (Method of Testing Connectors for Electronic Equipments). This is a method of: connecting electrical wires to a crimping terminal, and then gripping each of the ends of the thus-crimped terminal connected with the wires, to conduct a tensile test, thereby measuring the strength when broken. In general, at the crimped part, the caulking makes the sectional area of the conductor smaller by 20 to 30% than that of the conductor before the caulking (hereinafter, the percentage of a reduction in the sectional area of a conductor by caulking is referred to as the “sectional area reduction” (of the conductor)). Thus, the absolute value of the mechanical strength of the conductor is lowered at the crimped part. As a result, usually, the breakage occurs at the caulked part.
In the meantime, for example, in an automobile wiring circuit, the number of electrical wires to be used has been increased, since the electronic technology of controlling and the like has been advanced. Along with that, the total weight of the electrical wires therein has been increasing. However, the lightening of weights of automobiles has been required, from the viewpoint of energy saving. As a measure therefor, the diameters of conductors of electrical wires are required to be made small, thereby making the total weight of the electrical wires lightened.
However, although the above-mentioned annealed copper wire, which constitutes a conventional conductor of an electrical wire, has a room sufficient for electric conduction capacity, the copper wire is not easily made small in diameter. This is because the mechanical strength of the conductor of an electrical wire itself is small. Further, the crimping strength of the annealed copper wire at the crimped part is substantially equal to that at the non-crimped part, since the conductor itself may undergo work-hardening even when the sectional area of the conductor is decreased by caulking. Thus, the stability of the crimping strength is high, but the copper wire has a big problem that the strength thereof itself is low since the wire is made of annealed copper.
Thus, as a measure for enhancing the mechanical strength of the crimped part, study has been made on, for example, the use of a copper alloy hard material (see Patent Literature 1). Further, study has been made on the use of an age-precipitating copper alloy (of a Cu—Ni—Si-based, so called Corson alloy) in copper alloy wires which are excellent in flexure resistance, and which can decrease occurrence of wire-breakage due to tension at the crimped terminal part (see Patent Literature 2). Furthermore, study has also been made on improvement in properties of age-precipitating copper alloy wires (see Patent Literatures 3 and 4).